1. Field of the Invention
This invention relates generally to a system and method that provides air cooling for a battery and, more particularly, to a system and method that provides air cooling for an electric vehicle battery that employs flow-shifting.
2. Discussion of the Related Art
Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV) that combine a battery and a main power source, such as an internal combustion engine, fuel cell systems, etc., and electric only vehicles, such as the battery electric vehicles (BEV). All of these types of electric vehicles employ a high voltage battery that includes a number of battery cells. These batteries can be different battery types, such as lithium-ion, nickel metal hydride, lead-acid, etc. A typical high voltage battery system for an electric vehicle may include a large number of battery cells or modules including several battery cells to meet the vehicle power and energy requirements. The battery system can include individual battery modules where each battery module may include a certain number of battery cells, such as twelve cells. The individual battery cells may be electrically coupled in series, or a series of cells may be electrically coupled in parallel, where a number of cells in the module are connected in series and each module is electrically coupled to the other modules in series. Different vehicle designs include different battery designs that employ various trade-offs and advantages for a particular application.
The high voltage battery on an electric vehicle is typically mounted to a steel support plate and covered with a suitable protective cover that provides a number of functions. For example, the cover is a protective cover in that it prevents the battery cells from being damaged as a result of collision with other objects. Further, the cover provides electrical insulation from the high voltage of the battery to protect individuals and users. Also, the cover provides an EMI/RFI shield that absorbs radiation over a broad range of wavelengths from the high voltage battery caused by turning on and off various current flows, which otherwise could interfere with the vehicle radio, cell phone operation, etc.
Known battery systems for electric vehicles typically include a thermal management system that maintains the battery at a desirable operating temperature to increase the performance of the battery. The thermal management system typically includes a cooling fluid line and an associated heat exchanger within the battery enclosure, where the cooling fluid line directs a cooling fluid into the enclosure and to the heat exchanger to either heat the battery when it is at low temperature or cool the battery when it is at high temperature. The thermal management system also includes a reservoir that identifies the fluid level within the coolant management system.
It is know in the art to provide cooling and heating of a vehicle battery using air by providing a blower that blows heated or cooled air through the battery enclosure. Air cooling and heating provides a number of advantages over liquid cooling and heating including lower cost, lower complexity, higher reliability, etc. For example, it is not necessary to be concerned with fluid leakage in an air thermal management system. However, as the size of the battery increases, and thus, the heat load of the battery increases, the ability to use an air thermal management system is reduced. Particularly, the higher air flow required at higher heat loads may not provide the desired maximum difference in temperature (delta T) between cells in the battery pack and within each cell itself. In other words, battery durability and performance is increased for those battery packs that have a smaller difference in temperature from one cell to other cells and a smaller difference in temperature within a cell itself. By using air heating or cooling, the temperature of the cells at one end of the battery pack may have a significantly different temperature than those cells at an opposite end of the battery pack.
It is possible to overcome these problems in temperature differentials by providing a larger flow rate of air and/or a larger volume of air. However, increases in air flow rate and volume typically require larger fans and fan speeds, which requires greater power and causes more fan noise. Thus, for electric only vehicles that typically include larger batteries, air cooling and heating has typically heretofore not been viable. However, for the reasons given above, an air cooling and heating system that provides the proper cell delta T could still be desirable.